devel/electron39: Fix build with rust 1.94

The previous patch fixed builds with rust 1.95. However, it broke
builds with rust 1.94, which is the current version in the ports
tree. This commit makes it build with both rust 1.94 and 1.95.

Fixes: 9cffc4aeae6a (devel/electron39: Fix build with rust 1.95)